This invention relates to a temperature-measuring device for rotary kilns, comprising a stripping sleeve, which is rigidly mounted in a bore in the shell of the rotary kiln and protrudes to some extent into the rotary kiln, and a thermocouple, which is disposed in a protective tube, which is movably disposed in the stripping sleeve and secured to a lifting and lowering device, which is mounted on the outside of the shell.
In processes carried out in a rotary kiln, e.g., in the direct reduction of iron oxides below the melting and softening point of the charge by means of solid and gaseous reducing agents, the temperature must be exactly controlled throughout the length of the rotary kiln. The temperature is usually measured by means of thermocouples, which are disposed in protective tubes, which are spaced along the rotary kiln and extend through the wall and revolve with the kiln. Because the charge tends to cake on the protective tubes or to soil the same in the kiln, the resulting deposits must be removed from time to time because an error would otherwise be introduced into the result of the measurement.
A known temperature-measuring device for rotary kilns disclosed in German application P 21 32 687 comprises a thermocouple disposed in a protective tube, which is surrounded by a sleeve, except for its lower-most portion. The protective tube and the sleeve are secured outside the shell of the rotary kiln to a holder, which bears on a spring element, which is secured laterally of the protective tube. A roller is disposed above the spring element and during a rotation of the rotary kiln enters a cam track, which causes the roller to force the protective tube and sleeve into the interior of the furnace. As the roller leaves the cam track, the spring element returns the protective tube and the sleeve. The parts are depressed when they reach that range of the rotary kiln which contains the charge and are returned as they leave that charge-containing range. Whereas crusts can be knocked off the kiln wall by this device as it is forced into the kiln, it is not possible to remove crusts or dirt from the protective tube. Besides the fact that the protective tube and the sleeve are laterally secured and guided may easily result in canting.
For measuring temperature in the kiln atmosphere of kilns for making cement it is known from German application P 12 66 538 to arrange the thermocouple and the protective tube in a stripping sleeve, which is disposed in a guide sleeve. Outside the kiln, the stripping sleeve is secured to a bellcrank lever and the latter is secured to a crank drive. When it is desired to remove dust from the protective tube, the stripping sleeve is pushed into the kiln beyond the end of the protective tube and is then pulled out. As the stripping sleeve is pulled out, dust is removed also from the stripping sleeve as a result of its cooperation with the guide sleeve. The crank drive may be replaced by an eccentric mechanism or similar drive means, which directly strikes against a projection of the stripping sleeve, which is resiliently mounted. Whereas this arrangement can be used to remove dust which has been deposited from the kiln atmosphere, difficulties are involved in the use of the arrangement with rotary kilns. As the device moves through the charge, crusts are formed on the protective tube and when the stripping sleeve is pushed inwardly these crusts can easily be seized between the stripping sleeve and protective tube and may then cause destruction. Particularly the edge of the stripping sleeve tends to be damaged quickly and to burn off and there is also a danger of canting.
From "Neues aus der Technik", Vogel-Verlag, Wurzburg, No. 3, June 1, 1973, page 1, it is known to provide a thermocouple in a protective tube, to arrange the latter in a fixed sleeve, to secure the protective tube outside the rotary kiln to a toggle joint, which is loaded by a compression spring, and to control the toggle joint by a cam disc during the rotation of the rotary kiln. In this arrangement, the protective tube is pulled into the sleeve and cleaned and as it leaves the cam disc is pushed out on the sleeve by the spring pressure. In that case too, crusts formed on the protective tube can easily be seized between the sleeve and the protective tube as the latter is pulled into the sleeve so that damage results and specifically the edge of the sleeve is damaged and burns off. There is also a danger of canting in this arrangement.